The present invention relates to image forming apparatuses using the electro-photographic method, such as copiers, printers, and facsimile machines, and, in particular, relates to cleaning devices for removing the toner remaining on the image carrier.
An image forming apparatus is known which forms a toner image on a photoreceptor drum provided with, around it, various devices for charging, exposure, and development and which has a configuration for transferring the toner image onto a recording sheet, or a configuration for making a primary transfer of the toner images formed on plural photoreceptor drums onto an intermediate image transfer belt and then making a secondary transfer of the toner image on the intermediate image transfer belt onto a recording sheet. In this type of image forming apparatus, a cleaning apparatus for removing the toner remaining on the photoreceptor drum or on the intermediate image transfer belt without being transferred (hereinafter, they are called image carriers) by causing a blade made of a material such as urethane rubber to press against the image carrier in the direction counter to the direction of movement of the image carrier.
In this type of blade cleaning apparatus, since it is necessary to cause the cleaning blade to press against the image carrier with a force of a prescribed value to scrape off the remaining toner surely, friction is generated between the cleaning blade and the image carrier and this friction causes problems such as bending of the cleaning blade, damage to the cleaning blade edge, toner filming, and pitch variations of the image caused by changes in the image carrier driving force due to increased friction force.
When the remaining toner is removed from the image carrier by a cleaning blade, the remaining toner can be removed by the edge of the cleaning blade, but part of the toner remains on the edge. Abrasive particles contained in the toner become a lubricant and a small quantity of these particles enter the space between the edge and image carrier, whereby the friction coefficient between the cleaning blade and image carrier is reduced. This arrangement allows the remaining toner to be removed on a continuous basis without causing the blade to be curled up.
An invention has been proposed to make effective use of the aforementioned function, whereby the aforementioned problems are solved. To be more specific, paying attention to the remaining toner having been removed by the cleaning blade, this invention keeps the toner temporarily stored in a space provided in the vicinity of the cleaning blade, without recovering the remaining toner immediately, whereby the toner is always present on the edge of the cleaning blade (see Japanese Unexamined Patent Application Publication No. 2005-249915).
This arrangement provides the cleaning blade with lubricating ability without being affected by the printing span or printing ratio, and solves the problems related to curling of the cleaning blade, damage on the edge of the cleaning blade, toner filming or pitch irregularity of the image.
Referring to FIG. 1, the following describes the cleaning device disclosed in the Japanese Unexamined Patent Application Publication No. 2005-249915.
The reference numeral 601 denotes a casing, on which various members constituting the cleaning device are mounted.
The reference numeral 602 denotes a cleaning blade made of an elastic body such as urethane rubber. This blade is fastened onto the blade holder 603 by an adhesive or the like.
The blade holder 603 is rotatably supported by a supporting shaft 604 mounted on the casing 601.
The reference numeral 605 indicates a tension spring. It supplies bias in such a way that the blade holder 603 rotates in the counterclockwise direction. While the edge of the cleaning blade 602 faces in the direction (in the counter direction) against the rotational direction of the intermediate image transfer belt 70, pressure contact of the edge is applied to the intermediate image transfer belt 70 backed up by a backup roller 75 at the pressure contact position C.
The reference numeral 608 is a toner guide roller made of sponge. This roller contacts the intermediate image transfer belt 70 upstream of the pressure contact position C in the rotating direction of the intermediate image transfer belt 70. Further, at the position in contact with the intermediate image transfer belt 70, the toner guide roller 608 rotates to move in the same direction as the intermediate image transfer belt 70.
The reference numeral 609 is a toner ejection regulating member made of a PET sheet. One end thereof contacts the toner guide roller 608 at the position opposite to the contact position between the toner guide roller 608 and intermediate image transfer belt 70, and the other end is fixed on the holding member 610 mounted above the toner guide roller 608 by means of double-faced adhesive tape or the like.
The holding member 610 is fixed on the projection 611 of the casing 601 by means of screws.
The aforementioned structure forms a space S enclosed by an intermediate image transfer belt 70, cleaning blade 602, toner guide roller 608, and toner ejection regulating member 609.
The reference numeral 612 is a recovery screw provided on the bottom of the casing 601. The remaining toner stored on the bottom of the casing 601 is fed in the direction perpendicular to the sheet surface of the drawing, and is ejected out of the casing 601.
The reference numeral 613 is a toner receiving sheet made of PET (polyethylene terephthalate). The one end thereof is fixed to the bottom of the casing 601, and the other end contacts the intermediate image transfer belt 70 to ensure that the toner remaining inside the casing 601 does not fall down.
The operation of a cleaning device 60 will be described below.
After the toner image on the intermediate image transfer belt 70 has been subjected to secondary transfer onto the recording sheet, the toner remaining on the intermediate image transfer belt 70 is scraped off by the cleaning blade 602, and is stored in the space S. When the amount of toner stored in the space S has exceeded a predetermined level, toner is ejected from the contact position between the toner ejection regulating member 609 and toner guide roller 608, so that the amount of the remaining toner stored therein is kept constant. In other words, if there is an increase in the amount of the remaining toner stored in the space S, the function like that of a pressure regulating valve is implemented because the toner ejection regulating member 609 is elastic, whereby a predetermined amount of the remaining toner is kept in the space S.
Thus, the upper level of the remaining toner stored is always kept above the pressure contact position C. This arrangement ensures the remaining toner as a lubricant to be supplied to the edge of the cleaning blade 602, despite the continuous image formation of a lower printing ratio.
Further, despite continued image formation of the recording sheets having a smaller width, toner is made to expand across the recording sheet by the rotation of the toner guide roller 608 and a slight vibration of the apparatus, since the remaining toner is characterized by high fluidity. Thus, the toner is stored uniformly in the space S. This arrangement allows the toner to spread along the entire length of the cleaning blade, as viewed across the recording sheet width.
In an image forming apparatus provided with the aforementioned cleaning device disclosed in the Japanese Unexamined Patent Application Publication No. 2005-249915, the system speed may be changed. For example, the system speed is set at a lower rate when thick paper is to be fixed or when glossiness is increased on a recording sheet.
In this case, the peripheral speed of the intermediate image transfer belt 70 changes. At the same time, when the peripheral speed of the toner guide roller 608 changes, there will be a change in the amount of the remaining toner ejected from the space S, and this causes a change in the stored amount. If there is a shortage in the amount of the remaining toner stored in the space S, the edge of the cleaning blade 602 will be damaged or filming will occur to the intermediate image transfer belt 70. Further, an excessive amount of the remaining toner stored will cause toner packing to occur inside the space S, or allows the remaining toner to slip through the edge of the cleaning blade 602.
In view of the problems described above, it is an object of the present invention to adequately set the peripheral speed ratio of the toner guide roller with respect to the image carrier in conformity to the speed change of the system, and to keep the amount of the remaining toner stored in the space at a constant level, thereby prolonging the service life of the cleaning blade.